#include<stdio.h>
#include<math.h>
int main()
{
	double x, sum, i, b, c, d;
	b = 1.0000000;
	c = -1.000000; 
	sum = 0, i = 1, d = 1;
	do 
	{
		scanf_s("%lf", &x);
	} while (x <0.5 && x >1);
	for (; fabs(d) >1E-4; i++)
	{
		b *= x, c *= (-1);
		d = (b / (2 * i - 1) * c);
		sum += d;
	}
	printf("the sum is %.2lf", sum);




}